Organic light emitting display (OLED) has advantages of self-luminous, low drive voltage, high luminous efficiency, short response time, high definition and contrast, nearly 180° viewing angle, wide temperature range, flexible display and large area full color display, is recognized as the most promising display.
According to the drive mode, OLED displays can be divided into two categories: passive matrix OLEDs (PMOLED) and active matrix OLEDs (AMOLED), that is, direct addressing and thin film transistor (TFT) matrix addressing. Wherein the AMOLED display has a matrix arrangement of pixels, belonging to the active display type, high luminous efficiency, and is generally used for high-definition large-size display devices.
Since the AMOLED display is a current-driven display device, the uniformity and stability of the driving TFT affect the display effect. Specifically, the display brightness of each AMOLED pixel is uneven, and compensation is required. At present, the compensation technology for AMOLED in the industry includes internal compensation within the pixel and external compensation outside the pixel, wherein the external compensation is further divided into external optical compensation and external electric compensation. In the field of large-size AMOLED display, external electrical compensation technology is important. The principle is that the inhomogeneity of the TFT in the AMOLED pixel is obtained by the electrical detection method, and then the offset value is compensated at the pixel driving voltage. Therefore, the accuracy of the electrical detection directly affects the effect of the external electrical compensation.
Please also refer to FIG. 1 and FIG. 2, in the existing 3T1C structure of the external compensation pixel circuit, the first TFT T10 is a driving TFT for directly driving the organic light emitting diode D10; the second TFT T20 is a switching TFT for controlling the writing of the image data voltage Data; the third TFT T30 is a detecting TFT for writing a constant voltage Van to its own source in the display mode and detecting the voltage of the source s of the first TFT T10 in the detecting mode.
Please refer to FIG. 1, the existing external electrical compensation detection method ignores the cross-voltage between the gate and the source of the third TFT T30 in the display mode. It is considered that the voltage Vs of the source s of the first TFT T10 is equal to the constant voltage Vcm. However, since the cross-voltage Vds between the drain and the source of the third TFT T30 is not substantially 0, the voltage Vgs between the gate g and the source s of the first TFT T10 is not equal to the expected value, but the deviation is not taken seriously.
Please also refer to FIG. 1 and FIG. 2, the detection mode is divided into the potential resetting stage and the charging stage. The potential resetting stage still maintains the state shown in FIG. 1; after entering the charging stage, the second TFT T20 is turned off, the first TFT T10 flows through the current ID, and the current ID flows through the third TFT T30. At this stage, based on the detected voltage of the source s of the first TFT T10, the threshold voltage and the carrier mobility of the first TFT T10 can be calculated. The existing external electrical compensation detection method also ignores the cross-voltage between the drain and the source of the third TFT T30 in the detection mode. It is considered that the voltage Vsense detected at the source of the third TFT T30 is equal to the voltage of the source s of the first TFT T10. Strictly speaking, this omission inevitably brings about error, resulting in errors in the calculated threshold voltage and carrier mobility of the first TFT T10. The purpose of the present disclosure is to provide an AMOLED external electrical compensation detection method which can improve the accuracy of AMOLED external electrical compensation detection, improve the writing accuracy of gate-source voltage of the driving TFT in the display mode and reduce the calculation error of the threshold voltage and the carrier mobility of the driving TFT in the detection mode.